Various types of devices may require hermetic sealing to protect the active components from atmospheric elements, such as moisture and/or gases. For example, devices which include organic active elements such as OLEDs require protection from moisture or gases. OLED devices can serve as displays for various types of consumer electronic products, such as automobile stereo displays, cellular phones, cellular smart phones, personal organizers, pagers, advertising panels, touch screen displays, teleconferencing and multimedia products, virtual reality products and display kiosks.
Referring to FIG. 1, a conventional OLED device is shown. The OLED device comprises a functional stack formed on a substrate 101. The functional stack comprises one or more organic functional layers 102 between two conductive layers (104 and 106) which serve as electrodes. The conductive layers are patterned to form rows of cathodes in a first direction and columns of anodes in a second direction. OLED cells are located in the active region where the cathodes and anodes overlap. Charge carriers are injected through the cathodes and anodes via bond pads 108 for recombination in the functional organic layers. The recombination of the charge carriers causes the functional layers of the cells to emit visible radiation.
Active components, such as the cathode and organic layers in organic devices are adversely impacted by potentially deleterious components such as water, oxygen and other gaseous components. One approach is to hermetically encapsulate the device with a cap 110, sealing the cells. Typically, an epoxy based sealant 111 is used to bond the cap to the substrate. However, the sealant can be penetrated by potentially deleterious components such as moisture, oxygen and other gases. Small amounts of such deleterious components can be trapped in the encapsulation during the sealing process. Additionally, such deleterious components may diffuse into the encapsulation over time. This can adversely impact the reliability of the OLED device.
To improve the sealing of the encapsulation, a drying agent 114, such as barium oxide, calcium oxide or sodium oxide, may be provided. However, these compounds react with water only, and cannot serve to remove residual gases such as oxygen. Reaction with water disadvantageously forms products that will adversely impact the device layers if they are not packaged and separated from the device layers. The packaging material poses an additional barrier through which water and gases have to permeate to be absorbed, hence reducing the speed and efficiency of absorption. Such restrictions will also lead to bulkier OLED devices and a reduction in efficiency of the fabrication process. Drying agents such as zeolite or silica gel absorb mainly water and not reactive gases. At high temperatures, these drying agents disadvantageously discharge the absorbed moisture into the internal space of the OLED device.
As evidenced from the foregoing discussion, it is desirable to provide an improved method of encapsulating OLED devices to protect the device layers from potentially deleterious components such as water and reactive gases.